Method for the Conversion of Biomass to Liquid and/or Gaseous Energy Carriers

ABSTRACT

The invention relates to a method for the pyrolysis of a hydrocarbon-containing solid biomass for the obtention of liquid and/or gaseous energy carriers in the presence of a heat carrier, whereby a mixture of the heat carrier and the biomass is heated to the pyrolysis of the biomass. The method according to the invention is characterized in that the biomass is impregnated with a volatile, non-aqueous liquid before being mixed with the heat carrier.

The present invention relates to a method for the pyrolysis of ahydrocarbon-containing solid biomass for the obtention of liquid and/orgaseous energy carriers in the presence of a heat carrier, in which amixture of the heat carrier and the hydrocarbon-containing biomass isheated to the pyrolysis of the hydrocarbon-containing biomass.

Methods for the pyrolysis of biomass in the presence of a heat carrierare known.

In doing so, the pyrolysis can be performed with solid heat carriers(e.g., with sand in the form of a flash pyrolysis) or with liquid heatcarriers. The latter alternative is referred to as liquid-phasepyrolysis.

An important variant of the liquid-phase pyrolysis consists in using aheavy oil as a heat carrier. In said variant, a thermal cracking of theheavy oil occurs simultaneously during the pyrolysis of the biomass,whereby combustibles and fuels, respectively, are obtained in addition.

WO 2010/031803 A describes a method for the liquid-phase pyrolysis of ahydrocarbon-containing biomass with heavy oil as a heat carrier, whereina hydrocarbon-containing biomass is to be used the moisture content ofwhich amounts to, at most, 1.0% by weight, based on the biomass.According to WO 2010/31803 as well as WO 2008/034596 A1 and WO2008/11925 A1, the biomass can be impregnated prior to the pyrolysiswith the heat carrier (heavy oil), i.e., with the liquid with which alsothe pyrolysis is performed.

AT 508469 B1 describes a liquid-phase pyrolysis of a biomass, wherein abiological catalyst, which is a residual plant matter, is added.

DE 10 215679 A1 describes a method of a liquid-phase pyrolysis in atemperature range from 350 to 500° C. and under a system pressure of upto 100 bar. Solid zeolites and, in a supporting role, alkaline chemicalsare indicated as catalysts.

US 2009/0299112 A1 describes the processing of a biogenic raw materialcomprising a hydrocarbon via hydrogenation under high-pressureconditions.

Further methods are known, for example, from U.S. Pat. No. 4,266,083,U.S. Pat. No. 4,941,966, US 2007/0261996, US 2012/271074 and EP 0 027962 A2.

In particular during the liquid-phase pyrolysis of a biomass, i.e., thepyrolysis of biomass in a liquid carrier medium, a conversion of solidbiomass to a liquid, a solid and a gaseous phase occurs in thetemperature range from 300 to 450° C. If a hydrocarbon—e.g., anintermediate of a refinery such as a vacuum gas oil—is used as a carriermedium, the liquid phase will consist of a hydrophobic hydrocarbonfraction as well as a hydrophilic pyrolysis oil fraction.

In doing so, the objective is to transfer as much energy of the biomassas possible into the liquid and/or gaseous hydrocarbon fraction, forexample, through the transfer of biogenic carbon. The transfer rateincreases as the pyrolysis temperature rises, but, in general, is below20-30% by weight, based on the employed biomass. Thus, a furtherimprovement in the conversion of biomass to the desired fraction isdesirable.

In the literature, a temperature rise is suggested for this purpose, onthe one hand. However, especially in a liquid-phase pyrolysis, thetemperature rise is limited physically by the distillation range of thecarrier liquid due to the system pressure which is prevailing. At anoverpressure of typically <0.5 bar, the process temperature is thuslimited physically to a maximum of 450° C. With the temperature rising,the required energy input rises as well and the costs for operating theplant increase.

Alternatively, the use of zeolite-based catalysts, which are supposed toprovide a higher selectivity, is reported in the literature. However, inlaboratory testing, the use of solid catalysts has failed to produce anappropriate effect. Moreover, the subsequent use of the remaining coalwould thereby either deteriorate or else require a costly separation ofthe coal from the catalyst.

It is the object of the present invention to increase the rate of thetransfer of biogenic carbon into the liquid hydrocarbon fraction in ageneric method.

Said object is achieved by a method for the pyrolysis ofhydrocarbon-containing solid biomass for the obtention of liquid and/orgaseous energy carriers by means of pyrolysis in the presence of a heatcarrier, whereby a mixture of the heat carrier and thehydrocarbon-containing biomass is heated to the pyrolysis of thehydrocarbon-containing biomass, which is characterized in that thebiomass is impregnated with a volatile, non-aqueous liquid before beingmixed with the heat carrier.

SHORT DESCRIPTION OF THE FIGURES

FIG. 1 shows a process diagram of an embodiment of the method accordingto the invention.

FIGS. 2 and 3 show the results of the implementation of two comparativetests and of the implementation of the method according to the inventionin a laboratory system.

FIGS. 4 and 5 show the results of the implementation of a comparativetest and of the implementation of the method according to the inventionin a continuous pilot plant.

FIG. 6 shows a comparison of boiling point curves for the hydrocarbonsused in example 2 for impregnating the biomass.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that, by impregnating the biomass with a volatile,non-aqueous liquid before being mixed with the heat carrier and thusbefore the actual pyrolysis, the reaction processes on the particles ofthe biomass can be influenced positively in such a way that, at acomparable reaction temperature, an improved conversion toward theliquid and/or gaseous hydrocarbon phase will occur.

Undesirable secondary reactions can be suppressed by a shortened dwelltime of the reaction products in the hot, reactive phase (=liquid bath).From the literature, it is known that, in the dry flash pyrolysis,shorter dwell times lead to increased conversions toward a liquidproduct. However, especially in the liquid-phase pyrolysis, the heatingduration of the particle is in the range of minutes and cannot beaccelerated to any substantial degree, not even by optimal flowconditions.

It has now been found that, via impregnation with a liquid whichevaporates rapidly under reaction conditions (unlike the heat carrierwhich essentially does not evaporate at the reaction temperature), thelocal flow and mass exchange conditions are significantly improved andthe conversion is accelerated. A further positive effect is theentrainment of biogenic components from the surrounding carrier medium,which is improved by the evaporation of the liquid, whereby thosecomponents are no longer available for coking reactions, which possiblymight take place, and a larger concentration gradient between biomassparticles and carrier medium is created. In this way, the mass exchangeis again accelerated and the reaction is influenced positively in thedesired direction. As a consequence, less solid residue (coal) of thebiomass will remain upon completion of the pyrolysis.

According to the invention, the hydrocarbon-containing biomass isimpregnated with the volatile liquid before being mixed with the heatcarrier. In doing so, the biomass is preferably soaked continuously withthe volatile liquid in a first step, the excess amount is allowed todrip off, and the impregnated biomass is supplied continuously to thepyrolysis step.

In this way, the pores of the biomass are filled with the liquid. Theimpregnated biomass is mixed with the heat carrier which is essentiallyresistant against the high pyrolysis temperatures, and, as soon as thepyrolysis temperature is reached, a sudden evaporation of the volatileliquid takes place, resulting in a steam explosion effect within thepores.

The mass ratio of the volatile liquid to the biomass is therebypreferably 1.5 to 1 or less, particularly preferably 1:1 or less, basedon the mass of the dry biomass.

The volatile liquid shows a boiling behaviour according to which thefinal boiling point (95% evaporated) is lower than or, at most, equal tothe temperature of the pyrolysis step so that the volatile liquidevaporates essentially completely at the temperature of the pyrolysisstep.

Preferably, the volatile liquid has a final boiling point (95%) of 380°C. or less (in line with EN590). This applies in particular in case of aliquid-phase pyrolysis, using, for example, heavy oil as a heat carrier.

In case of a solid-phase pyrolysis, e.g., with a sand bed as a heatcarrier, wherein pyrolysis temperatures of, e.g., 550° C. occur, aliquid with a correspondingly higher final boiling point can also beused as a volatile liquid.

Particularly preferably, the volatile liquid is a hydrocarbon mixturewith a content of aromates of 1% or more.

The volatile liquid can be selected in particular from the groupconsisting of light gas oil (LCO or LGO), diesel, petrol and mixturesthereof. A person skilled in the art understands a light gas oil to be aprecursor of middle distillates such as diesel fuel and extra-lightheating oil, which is derived directly from the fractionation of crudeoil and the boiling temperature of which is between 190 and 400° C.

Particularly preferably, a refinery intermediate is used as the volatileliquid.

If a volatile intermediate of refinery is used (e.g., LCO, crude diesel(light gas oil LGO), crude petrol), it is possible to deliberatelyinfluence the biogenic amount in a desired boiling range, e.g.,preferably toward diesel, toward kerosine or toward petrol,simultaneously improving the transfer of biogenic carbon into the liquidphase. Ideally, fractions from the refining area can thus be applied infields for which they were previously unsuitable (e.g., the use of LCOin the fuel fraction).

The gases formed during the pyrolysis can be removed in a manner knownper se and can be condensed for obtaining the liquid energy carriers or,respectively, can be separated further into the desired fractions.

The pyrolysis process can be performed at an overpressure of 0.5 bar orless.

According to a further preferred embodiment of the present invention,the pyrolysis is carried out in the form of a liquid-phase pyrolysis.The problems arising especially in connection with a pyrolysis ofbiomass in the form of a liquid-phase pyrolysis have already beendiscussed hereinabove.

In said embodiment, particularly preferably a heavy oil, in particular avacuum gas oil, is used as a heat carrier, and thus a liquid-phasepyrolysis is performed, with the heavy oil being thermally cracked atthe same time.

In said embodiment, the pyrolysis step of the method according to theinvention is typically carried out at temperatures of 300-450° C. and atan overpressure of, at most, 0.5 bar. The quantitative proportionbetween the biomass and the heavy oil is typically in the range of 1:2.

In the following, preferred embodiments of the invention are illustratedin further detail on the basis of the figures as well as the exemplaryembodiments:

According to FIG. 1, an optionally moist hydrocarbon-containing biomassBM is pretreated (PT) mechanically and/or thermally. For example,moisture (M) present during the pretreatment can be removed.

In the preferred embodiment shown in FIG. 1, an impregnation I of thepretreated biomass with a volatile liquid FL is provided subsequently.Also in this step, moisture M may be removed from the biomass as aresult of the impregnation. In a first separator S1, excess liquid FL isremoved from the biomass and returned to the impregnation step I.

The impregnated biomass is supplied continuously to a reactor R. A heatcarrier HC, in the preferred embodiment of the invention a heavy oil, isalso supplied to the reactor. In the reactor R, a pyrolysis is performedin a manner known per se at temperatures typically ranging from 300° C.to 550° C. and at a slight overpressure (e.g., up to 450° C. and at anoverpressure of, at most, 0.5 bar), whereby the volatile liquid presentin the pores of the biomass escapes abruptly. The vapours of the reactorreach a condenser K. Gaseous components are collected as a gas G. Thecondensed components reach a second separator S2 and are separated thereinto oily fractions O and aqueous fractions W.

In a third separator S3, the bottom product of the reactor R is splitinto solid products (SO) and a heat carrier, with the latter beingreturned to the reactor R as the heat carrier HC.

Example 1

A laboratory test was performed at a reaction temperature of 370° C. andan overpressure of about 0.05 bar, using spruce wood as a biomass withvacuum gas oil as a carrier medium. As a reactor unit, a stirrer vesselheated from the outside was used on a laboratory scale with an adjacentcondenser unit.

For a first comparative test (indicated by “NO” in FIGS. 2 and 3),approx. 100 g wood was predried and supplied conventionally withoutprevious impregnation to the laboratory reactor, with vacuum gas oil asthe carrier medium (ratio of vacuum gas oil to biomass 5:1). Uponcompletion, the arising liquid and solid products were separated andweighed. The resulting gases being still condensable were calculatedfrom a mass difference to the biomass employed. As the products ofpyrolysis, solid coal, a liquid pyrolysis oil not miscible with waterand comprising reaction water as well as a hydrocarbon-soluble liquidproduct fraction were formed.

As a further comparative test (indicated by “VGO” in FIGS. 2 and 3), dryspruce wood was impregnated with vacuum gas oil at about 60° C. at amass ratio of 1:1 and subsequently supplied to the laboratory reactor.Upon completion, the arising liquid and solid products were separatedand weighed. The resulting gases being still condensable were calculatedfrom a mass difference to the biomass employed.

In the test according to the invention (indicated by “LGO” in FIGS. 2and 3), the biomass was dried, subsequently impregnated with diesel fuel(mass ratio of approx. 1:1) and treated with vacuum gas oil in theliquid-phase reactor, as in the comparative tests.

In the method according to the invention, the result indicatesconsiderably less coal formation (R) and hence more mass transfer of thesolid biomass into the desired liquid and gaseous fractions (C).

Looking at the mass transfer of solid biomass into the hydrocarbonfraction, the result is even more distinct. Using a low-boilinghydrocarbon (LGO) according to the invention, the conversion could beincreased from about 10% by weight to almost 17% by weight. Using ahigh-boiling hydrocarbon for the impregnation (VGO), a conversion ofonly about 14% by weight was achieved. Hence, the use of the low-boilingliquid (LGO) according to the invention resulted in a 16% increase, ascompared to the use of the high-boiling liquid (VGO).

FIG. 2 shows the mass conversion of solid biomass to liquid as well asgaseous products (C) and the remaining solid material (R) of example 1.Left-hand side: comparative test without impregnation (NO). Middle:comparative test with a high-boiling vacuum gas oil (VGO). Right-handside: a test according to the invention with low-boiling gas oil (LGO).

FIG. 3 shows the mass transfer (“BtL”) of solid biomass to thehydrocarbon fraction—i.e., the mass fraction of liquefied biomass whichis miscible with hydrocarbons—of example 1. Left-hand side: comparativetest without impregnation (NO). Middle: comparative test with ahigh-boiling vacuum gas oil (VGO). Right-hand side: a test according tothe invention with low-boiling gas oil (LGO).

Example 2

In a continuous pilot plant, about 60 kg/h of dry spruce wood wassubjected to a pyrolysis at approx. 375° C. In doing so, vacuum gas oilwas used as a heat carrier medium at a ratio to the biomass of approx.4:1. The arising liquid and solid pyrolysis products were detected intheir mass flow and analysed for their content of biogenic carbon bymeans of the radiocarbon method (C14).

As a comparative test, the biomass was initially impregnated with vacuumgas oil (VGO) at approx. 150° C. (mass ratio of approx. 1:1) andsubsequently subjected to a pyrolysis step. The amount of solid residue(R) forming as a coal was determined, and its content of biogenic carbonwas detected via C14 measurement. In this way, a conversion of solidbiomass to liquid and gaseous products of about 64%, and, respectively,a transfer of biogenic carbon to liquid and gaseous products of 57%could be determined.

In a test according to the invention, the biomass was impregnated withlight gas oil (LGO) at about 120° C. (mass ratio of approx. 1:1) andsubsequently subjected to a pyrolysis step. The amount of solid residue(R) forming as a coal was determined, and its content of biogenic carbonwas detected via C14 measurement. In this way, a conversion of solidbiomass to liquid and gaseous products of about 67%, and, respectively,a transfer of biogenic carbon to liquid and gaseous products of 61%could be determined. Using a volatile liquid according to the invention,the conversion of the pyrolysis from a solid biomass to the desiredproducts could thus be increased demonstrably also in a continuous pilotoperation.

FIG. 4 shows the mass conversion of solid biomass to liquid as well asgaseous products (C) and the remaining solid material (R) of example 2.Left-hand side: comparative test with a high-boiling vacuum gas oil(VGO). Right-hand side: a test according to the invention withlow-boiling gas oil (LGO).

FIG. 5 shows the mass transfer (T) of biogenic carbon to liquid as wellas gaseous fractions of example 2. Left-hand side: a comparative testwith a high-boiling vacuum gas oil (VGO). Right-hand side: a testaccording to the invention with low-boiling gas oil (LGO).

FIG. 6 shows the boiling point curves of the hydrocarbons used inexample 2 for impregnating the biomass: Top part: high-boiling vacuumgas oil (VGO). Bottom part: low-boiling gas oil (LGO).

1. A method for the pyrolysis of a hydrocarbon-containing solid biomassfor the obtention of liquid and/or gaseous energy carriers in thepresence of a heat carrier, whereby a mixture of the heat carrier andthe biomass is heated up to pyrolysis of the biomass, characterized inthat the biomass is impregnated with a volatile, non-aqueous liquidbefore being mixed with the heat carrier.
 2. A method according to claim1, wherein the volatile liquid exhibits a final boiling point (95%)lower than or, at most, equal to the temperature of the pyrolysis step.3. A method according to claim 2, wherein the volatile liquid exhibits afinal boiling point (95%) of 380° C. or less.
 4. A method according toclaim 1, wherein the volatile liquid is a hydrocarbon mixture with acontent of aromates of 1% or more.
 5. A method according to claim 4,wherein the volatile liquid is selected from the group consisting of gasoil (LCO/LGO), diesel, petrol and mixtures thereof.
 6. A methodaccording to claim 5, wherein a refinery intermediate is used as thevolatile liquid.
 7. A method according to claim 1, wherein the massratio of the volatile liquid to the biomass is 1.5 to 1 or less based onthe mass of the dry biomass.
 8. A method according to claim 1, whereinthe pyrolysis is performed at an overpressure of 0.5 bar or less.
 9. Amethod according to claim 1, wherein the pyrolysis is carried out in theform of a liquid-phase pyrolysis.
 10. A method according to claim 9,wherein a heavy oil, in particular a vacuum gas oil, is used as the heatcarrier of the liquid-phase pyrolysis.
 11. A method according to claim7, wherein the mass ratio of the volatile liquid to the biomass is 1:1or less based on the mass of the dry biomass.